Performance of InxGa1-xAsyP1-yphotodiodes with dark current limited by diffusion, generation recombination, and tunneling

We present a theoretical study of the effects of diffusion, generation-recombination (GR), and the recently observed tunneling currents on the performance of photodiodes made from In0.73Ga0.27As0.63P0.37and In0.53Ga0.47As. Calculations are made for both p+ν and p-i-n punch-through diode configurations, and are compared with recent measurements made by several independent investigators. For doping densities typical of present material (N_{D} gsim 10^{15}cm^-3), tunneling currents become dominant prior to avalanche breakdown. Thus, for detection of weak (-55 dBm at 45 Mbits/s) optical signals, the diodes must be operated at low voltages where GR is the dominant source of reverse-biased leakage. To meet the requirements of low capacitance (C leq 0.5pF for a diode area of 10^-4cm²) and low GR dominated dark current (I_{D} leq 10nA atT = 70degC), the doping density and effective carrier lifetime (τeff) must beN_{D} < 7 times 10^{15}cm^-3andtau_{eff} gsim 150ns for In0.73Ga0.27As0.63P0.37and5 times 10^{14} lsim N_{D} lsim 7 times 10^{15}cm^-3andtau_{eff} gsim 3.5 mus for In0.53Ga0.47As.     

Electrooptical effects in silicon

A numerical Kramers-Kronig analysis is used to predict the refractive-index perturbations produced in crystalline silicon by applied electric fields or by charge carriers. Results are obtained over the1.0-2.0 mum optical wavelength range. The analysis makes use of experimental electroabsorption spectra and impurity-doping spectra taken from the literature. For electrorefraction at the indirect gap, we findDelta n = 1.3 times 10^{5}atlambda = 1.07 mum whenE = 10^{5}V/cm, while the Kerr effect givesDelta n = 10^{-6}at that field strength. The charge-carrier effects are larger, and a depletion or injection of 10¹⁸carriers/cm³produces an index change ofpm1.5 times 10^{-3}atlambda = 1.3 mum.     

Measurements of the electrooptic effect in CdS, ZnTe, and GaAs at 10.6 microns

Low-frequency electrooptic coefficients have been measured for three semiconductors at 10.5 microns. The results arer_{c} = (5.5 pm 1) times 10^{-12}m/V for CdS,r_{41} = (1.4 pm 0.2) times 10^{-12}m/V for ZnTe, andr_{41} = (1.6 pm 0.1) times 10^{-12}m/V for GaAs. A comparison is made of the efficiencies of these materials in different modulator configurations. The effect of photoelectrically induced space charge is discussed briefly.     

Study of the XeCl laser pumped by a high-intensity electron beam

We present the results of a detailed experimental study of the XeCl laser pumped by a high-intensity electron beam. The laser system was optimized as an oscillator for mixtures of Xe and HCl with Ne, Ar, and Kr diluents. The peak intrinsic efficiency (laser energy out/electron-beam energy deposited) was near 4.5 percent for each of these diluents. Small-signal gain and background absorption were measured as a function of electron-beam deposition rate from 0.4 to 6 MW/ cm³. The ratio of small-signal gain to absorption was found to be constant over this range with a value of ∼5. Measurements of absorption in the presence of a large photon flux indicated that there was no appreciable saturable contribution to the absorption. Measurements of fluorescence from theBandCstates indicate that collisional mixing between these states is very rapid. The formation efficiencies of theBandCstates are estimated to be 0.15 and 0.05, respectively. A vibrational relaxation rate of between 1 and1.5 times 10^{-10}cm³. s^-1was determined. The effect of this finite relaxation rate is to reduce the energy available to the stimulated process by a factor of 0.67-0.75. Estimates of the XeCl* deactivation rates by HCl and electrons were also obtained. A value of1.7 times 10^{-9}cm³. s^-1was obtained for quenching by HCl, and a value ofsim 1 times 10^{-7}cm³. s^-1was estimated for electron deactivation.     

Electronic processes at grain boundaries in polycrystalline semiconductors under optical illumination

The dependence of minority carrier lifetime (τ) on the doping concentration Nd, grain sizedand interface state density Nisat the grain boundaries in (n-type) polycrystalline semiconductors has been calculated analytically. The recombination velocity at grain boundaries is enhanced by the diffusion potential Vdadjacent to the boundaries, and ranges fromsimeq 10^{2}to 10⁶cm . s^-1depending on Nisand Nd. Under illumination, the population of the interface states is altered considerably from its dark level and as a result, Vddecreases to that value which maximizes recombination (equal concentrations of electrons and holes at the boundary). This causes τ to decrease with increasing Nd. Sample calculations for polycrystalline silicon show that for low angle boundaries with interface state densities ofsimeq 10^{11}cm^-2eV^-1, τ decreases from 10^-6to 10^-10s as the grain size is reduced from 1000 to 0.1 µm (forN_{d} = 10^{16}cm^-3). For a constant grain size, τ decreases with increasing Nd. The open-circuit voltage of p-n junction solar cells decreases fortau leq 10^{-7}s, whereas that for Schottky barrier cells remains at its maximum value untiltau lsim 10^{-8}s.     

Electromigration and low-frequency resistance fluctuations in aluminum thin-film interconnections

Low-frequency noise spectra originating from resistance fluctuations in Al films during electromigration were measured in the absolute temperature and current density intervals327 leq T leq 396K and1.34 times 10^{6} leq j leq 2.22 times 10^{6}A/cm². The values of SR, the resistance power spectral density, at 20 × 10^-3Hz allowed the construction of an Arrhenius plot from which a grain-boundary activation energy value of about 0.6 eV was deduced. This value lies in the range of values found by other authors using different techniques. A first attempt to model the observed dependence of SRonjandTis also described.     

Spectroscopy and lasing of a high Nd concentration Al-phosphate glass

An Al-phosphate glass containing Nd³⁺in concentrations ranging from3 times 10^{20}to2.7 times 10^{21}ions/cm³has been prepared and investigated spectroscopically. Different ways of measuring the⁴F3/2→⁴I9/2emission cross sections yield values between1.96 times 10^{-20}and2.7 times 10^{-20}cm². At the highest concentration the decay time is 50 μs, while the radiative lifetime is estimated to begeq446 mus. Lasing experiments were performed by pumping thin platelets of glass coaxially with a dye laser. Cross sections, losses, and differential efficiencies are derived from these experiments. The status of high concentration glasses versus stoichiometric Nd compounds is reviewed.     

Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2line

Experimental results are shown on the frequency stabilization of a GaAlAs laser using a Doppler-free spectrum in the saturated absorption of the Cs-D2line at 852.1 nm. The frequency stability (Allan variance) between3.0 times 10^{-12}and1.0 times 10^{11}was obtained at the averaging time between 0.1 and 1000 s.     

Growth, optical properties, and CW laser action of neodymium-doped gadolinium scandium aluminum garnet

Investigation of the congruent melting rare-earth aluminum garnet Gd3Sc2Al3O12(GADSCAG) has been made. The optimum crystal growth parameters for the undoped material are a rotation rate of 20 r/min and a growth rate of 4.6 mm/hr along thelangle111rangledirection. For Nd³⁺-doped crystals the linear growth rate is 2 mm/h. The optical properties of Nd:GADSCAG which are of interest for laser operation were also determined. The stimulated emission cross section of the 1.06-μ transition in Nd³⁺at room temperature is(3.2 pm 0.3) times 10^{-19}cm², the fluorescence lifetime is256 pm 8 mus at an Nd³⁺ion density of 1 atomic percent in the crystal and the integrated peak absorption cross section in the strongest pump band (0.81 μ) is3.8 times 10^{-19}cm², A comparison of the CW laser performance of identical ND:YAG and Nd:GADSCAG rods is presented.     

Antenna impedance measurements and sheath effects in an RF generated plasma

A device using an RF discharge quasi-homogeneous plasma to measure antenna impedance is described. The plasma diagnosis is done by using a new probe made of a transparent resonant cavity. The electron densities (2 times 10^{8}to6 times 10^{9}particles/cm³) and collision frequencies (6 times 10^{7}to1.5 times 10^{8}per second) are controlled by the discharge power. The density distribution measurements indicate a quasi-homogeneous region of 20 by 20 by 14 cm. Impedance measurement results are given for a a thick unipole between 100 and 750 MHz. The values ofX = (omega_{p}/omega)^{2}range from 0 to 44. They agree fairly well with Deschamps model theory applied to scaled frequency measurements as well as to a quasistatic simple analytical formula. Sheath effects enhanced by a dc bias are observed especially at low frequencies and the sheath thickness increase is calculated and found consistent with Pavkovich's parabolic potential assumption. The possibility of electronic tuning by a suitable bias is suggested.     

Solid-phase epitaxial Pd/Ge ohmic contacts to In1-xGaxAsyP1-y/InP

A Pd/Ge metallization to InGaAsP/InP semiconductors, formed with solid-phase epitaxy (SPE) technique, has been investigated in this study. With this method, ohmic contacts with low specific contact resistance (rho_{c} approx 2.3 times 10^{-6}Ω.cm²) have been achieved on p-type In0.53Ga0.47As(p approx 1.8 times 10^{19}/cm³). The same contact scheme also gives low specific contact resistance (rho_{c} approx 6 times 10^{-7}Ω.cm²) on n-type In0.53Ga0.47As (n approx 1.0 times 10^{19}/cm³). Excellent surface morphology is observed in all the samples, and the contacts do not deteriorate for at least 4 h at temperatures between 300 and 500°C.     

Impact ionization in bulk GaAs high field domain

An investigation of impact ionization in the high field domains of GaAs Gunn effect devices has been carried out. A method of measuring the number of excess electrons generated per domain transit was developed, based on the measurement of the increase in the valley current from one domain transit to the next while impact ionization is occurring in the domain. This method was used to experimentally determine the carrier generation per domain transitDelta n/n_{0}as a function of excess domain potential VDfor three material carrier concentrations. These results are compared to a theoretical calculation ofDelta n/n_{0}based upon an approximate solution of the continuity equation and invariant domain calculations. The experimental and theoretical results agree to within 2 percent forn_{0} = 3 times 10^{14}cm^-3and 6 percent forn_{0} = 4 times 10^{14}cm^-3.     

Ellipse rotation studies in laser host materials

Using a TEM00qnear Gaussian mode ruby laser system we report the first experimental measurements of intensity induced changes of optical polarization (ellipse rotation) in a cubic crystalline medium, YAG, for which we obtain the nonlinear susceptibilitieschi_{3}^{1221} (- omega, omega, omega, -omega) = 6.34 times 10^{-15}ESU andfrac{1}{2} (chi_{3}^{1111} + chi_{3}^{1221} - 2chi_{3}^{1212}) = 7.18 times 10^{-15}ESU, accurate to better than ±7 percent relative tochi_{3}^{1221} (- omega,omega,omega, -omega)for liquid CS2. These values are compared with further results obtained for fused quartz and two laser glasses. Moreover, by time resolving the ellipse rotation data we demonstrate the capability to plot ellipse rotation versus input power on a single laser shot, thus increasing the practical feasibility of the technique and introducing the possibility of resolving transient contributions to the measurement.     

Optimum design for high-power and high-efficiency GaAs Hi-Lo IMPATT diodes

Optimum structure parameters of GaAs hi-lo IMPATT diodes to give a high-efficiency and a high-output power are experimentally determined in the frequency range from 7 to 18 GHz. The highest efficiency is obtained at any frequency when a diode has a punch-through factor of about 0.6 and is depleted with an electric field strength of 10 kV/cm at the end of the lo region under operation. The optimum lo-region carrier concentration to achieve the highest efficiency and the upper limit of a junction area to obtain a high-output power without decreasing efficiency are found to be simply related to frequency by the following equations:(N_{L})_{opt} = (4 times 10^{14}) cdot (f/7)^{3}cm^-3and(S_{j})_{max} = (20 times 10^{-4}) cdot (f/10)^{-1.9})cm²), respectively, wherefis in gigahertz.     

FM eliminated CH4locked frequency stabilization of 3.39 µm He-Ne laser in dual feedback control

The frequency of the 3.39 μm He-Ne laser was locked to the CH4saturated absorption line by means of integral-proportional feedback control, i.e., dual feedback control. The frequency modulation was applied by a vibrating mirror placed outside a laser cavity, obtaining a modulation-free laser beam with a stabilized frequency. The long-term stability achieved under integral feedback control was aboutpm1.1 times 10^{-11}, which was further improved topm1.35 times 10^{-12}under dual feedback control. The Allan variance measured by the photomixing technique was1.77 times 10^{-12}at an averaging time 100 s.     

FM eliminated CH4locked frequency stabilization of 3.39 µm He-Ne laser in dual feedback control

The frequency of the 3.39 μm He-Ne laser was locked to the CH4saturated absorption line by means of integral-proportional feedback control, i.e., dual feedback control. The frequency modulation was applied by a vibrating mirror placed outside a laser cavity, obtaining a modulation-free laser beam with a stabilized frequency. The long-term stability achieved under integral feedback control was aboutpm1.1 times 10^{-11}, which was further improved topm 1.35 times 10^{-12}under dual feedback control. The Allan variance measured by the photomixing technique was1.77 times 10^{-12}at an average time 100 s.     

Continuously tunable sum-frequency generation involving sodium Rydberg states

Broadly tunable sum-frequency generation has been observed in a vapor of atomic sodium in the presence of a dc electric field. This field induces achi^{(2)}nonlinearity which is resonantly enhanced when the sum frequency corresponds to the energy separation between the ground state and an atomic Rydberg state. In a vapor of number density4 times 10^{14}cm^-3, we obtain an energy conversion efficiency as large as3 times 10^{-4}and achi^{(2)}as large as1.2 times 10^{-8}ESU. We have also observed sum-frequency generation in the absence of an applied dc field, and we relate these observations to mechanisms that have been proposed to explain this effect.     

Characteristics in InGaAs/InP avalanche photodiodes with separated absorption and multiplication regions

Improved characteristics of compound semiconductor avalanche photodiodes with separated absorption and multiplication regions (SAM) are discussed. Temperature dependences of dark current and breakdown voltage show that the tunneling current in the narrow energy gap layer can be suppressed in InGaAs/InP APD's with the SAM structure. Dark currents above punch-through voltages, at which the depletion layer reaches the InP-InGaAs heterointerface, are caused by the generation-recombination process in the InGaAs and at the heterointerface. Dark currents near breakdown depend on the n-layer thickness and are strongly affected by the electric field strength in the ternary layer. Tunneling currents are dominant in diodes with thin n-InP layers, while the generation-recombination processes in the InGaAs layers are dominant in those with a thick n-InP layer. The dark current was as low as7.8 times 10^{4}A/cm²atM = 10when the interface electric field strength is reduced. A maximum multiplication factor of 60 was observed for the6 times 10^{-7}A initial photocurrent. Rise time and full width at half maximum in a pulse response waveform were 100 and 136 ps, respectively, atM = 10.     

Excitation mechanism and plasma parameters in pulsed argon-ion lasers

Pulsed argon-ion lasers show several interesting properties at high currents. To understand the inversion mechanism, the plasma parameters, electrical conductivity, electron temperature, and electron density were measured with the double-probe method for the pressure range from 15 to 50 mtorr in a 6-mm-bore tube. When the discharge current increases from 100 to 700 amperes at the optimum pressure for laser oscillation, these parameters increase from 250 to450Omega^{-1}cdotcm^-1, from8 times 10^{4}to10^{5}degK, and2 times 10^{14}to 10¹⁵cm^-3, respectively. At the maximum electron density, the percent of ionization appears to be in excess of 100 percent, as a result of the pinch effect and double ionization. It is certain that this ring discharge is at least ionized very strongly. In a 10-mm-bore tube, only the electron temperature and density were measured. The current dependence of the laser output power at high currents is interpreted with those results. Excitation mechanisms of high-current argon-ion lasers are discussed with experiments and theories for strongly ionized plasmas.     

Dielectric breakdown threshold, two-photon absorption, and other optical damage mechanisms in diamond

The breakdown threshold and two-photon absorption coefficient are measured in diamond with picosecond pulses at 1.06 and 0.53 μm. The rms breakdown threshold at 1.06 μm is 21.5 MV/cm. The two-photon absorption coefficient at 0.53 μm is less than2.6 times 10^{-4}cm/MW.